Avaliação de bioestimulantes em sementes de alface: aplicação de análise de componentes principais e clustering

Abstract

The growing demand for healthy foods is driving lettuce cultivation, requiring practices that ensure productivity and quality. To achieve this, it is essential to adopt effective strategies from the initial stages of cultivation. In this context, seed imbibition combined with the use of plant biostimulants stands out for accelerating and standardizing germination, favoring more vigorous plant establishment. Given the complexity of the data generated, multivariate analysis has facilitated interpretation and is essential for interpreting the results in an integrated and accurate manner. This study aimed to evaluate the physiological potential of lettuce seeds subjected to different concentrations and periods of imbibition with biostimulants. It also validated the applicability of multivariate analysis using principal component analysis (PCA) and cluster analysis (dendrogram). This analysis aimed to identify groups of treatments with similar physiological responses and enable a more accurate classification of the effects of biostimulants. The experiments were conducted at the Phytotechnics Laboratory (CECA-UFAL) with crisp lettuce seeds treated with two biostimulants (seaweed extract and synthetic plant hormones) diluted in distilled water at concentrations of 0 (control), 4, 8, 12 and 16 mL.L−1. The seeds were soaked in the solutions for 8 and 16 hours, being incubated in a B.O.D. chamber at 20 °C. The following variables were evaluated: germination (G), first germination count (FGC), germination speed index (GSI), average germination time (AGT), synchrony index (ISG), length (SL) and seedling dry mass (SDM). The design was completely randomized (CRD), in a 5 × 2 factorial scheme (concentrations × periods), with four replicates of 25 seeds. The software RStudio (v. 4.4.1) and the packages Easynova, ExpAnalysis3D, GGally, and ggplot2 were used. The results showed that seaweed extract was most effective in terms of G and GCF in lettuce seeds after 8 hours of imbibition, particularly at concentrations of 4 and 16 mL.L−1. Higher concentrations and times negatively affected GSI and AGT. The highest GSI occurred after 16 hours at concentrations of 8 and 12 mL.L−1. Using the correlation matrix data, it was observed that germination strongly correlated with the other variables. For synthetic plant hormones, the best G, GSI, and AGT results were obtained with 4 mL.L−1 for 8 hours. Extreme concentrations and short or long periods negatively affected GCF. The GBI was higher between 8 and 16 hours at intermediate concentrations. The correlation matrix revealed negative relationships between some variables. PCA data showed that synthetic plant hormones at 4 and 12 mL.L−1 and seaweed extract at 4 mL.L−1 were more effective. The dendrogram results showed that treatments with 4 mL.L−1 of biostimulants for 8 hours presented more similar physiological responses, while concentrations of 8 and 16 mL.L−1 for synthetic hormones demonstrated greater dissimilarity. Therefore, it was concluded that the 8-hour imbibition period provided the best results, regardless of the biostimulant used. The seaweed extract was most effective at concentrations of 4 and 16 mL.L−1, while the synthetic hormones excelled at 4 and 8 mL.L−1. Multivariate analyses (PCA and dendrogram) were essential to identify response patterns and the most effective treatments. Keywords: Seaweed; Multivariate analysis; Dendrogram; Imbibition; Plant hormones.